Yes, I could not find a useful manual page here either, but I can show it on a screenshot:The hybrido emitter creates particles with a certain density/resolution depending on the sampling rate on the surface of the fluid or in the core. The "bandwidth" parameter is the thickness of this surface layer, anything more inside is considered core. Here on the screenshot both are set to 2, but you could use a much higher value for the surface and see more details in this region of the fluid. I am not a Houdini user, but this sounds similar to their system, I think.